The Web sites of the presidential office, the Office for Government Policy Coordination and some of the ruling Saenuri Party's municipal and provincial chapters have been cyber attacked.
Internet servers of some news agencies, including the Chosun Ilbo, have also been attacked.
At the time of the hacking attack on the Web site of the presidential office at around 9:30 a.m. Tuesday, the home page showed a message in red reading "Great leader Kim Jong-un," the North Korean leader.
For ten minutes from 10 a.m., another message appeared on the top office's Web site reading, "We Are Anonymous. We Are Legion. We Do Not Forgive. We Do Not Forget. Expect Us." It is, however, unclear who is behind the attack. Anonymous says it was not responsible.
The presidential office's home page was partially restored Tuesday afternoon.
Shortly after the hacking, the government issued its lowest level-one alert against cyber attacks on the nation's four-tier warning system. Later in the day, the warning was upgraded by one notch.
The presidential office is analyzing the pattern of the hacking to trace the origin of the attack.
Some have pointed to the possibility that the attacks could be a retaliation after Anonymous said it would hack into 46 North Korean portals on Tuesday.